1. Field of the Invention
The present invention relates to an illumination device and, more particularly, to an illumination device used in, e.g., a flash light emission apparatus used for taking a photograph.
2. Related Background Art
FIG. 16 is a schematic perspective view showing the arrangement of a camera comprising a conventional illumination device. The camera shown in FIG. 16 is constituted by a camera main body 6 comprising a phototaking lens 7 and an illumination device 10. In order to eliminate a red eye phenomenon (a phenomenon in which when the pupils of the eyes are open, a light beam emitted from the illumination device 10 is reflected by the fundi of the eyes, and the eyes are imaged in red), the illumination device 10 is aligned so that its optical axis 9 is sufficiently separated from an optical axis 8 of the phototaking lens 7. In general, when the camera main body 6 is viewed from the object side, the illumination device 10 is aligned at the right or left end of the camera main body 6, as shown in FIG. 16.
FIG. 17 is a schematic sectional view showing the arrangement of the illumination device shown in FIG. 16. Referring to FIGS. 16 and 17, the illumination device 10 comprises, e.g., a xenon tube 1 as flash light means for emitting flash light. A reflector 2 for reflecting a light beam radiated from the xenon tube 1 is arranged on the side opposite to an object with respect to the xenon tube 1.
On the other hand, on the object side with respect to the xenon tube 1, a Fresnel lens 3 for projecting a light beam directly radiated from the xenon tube 1 and a light beam reflected by the reflector 2 in the direction of an object is arranged. The Fresnel lens 3 has a rotation-symmetrical shape about its optical axis. A surface, facing the xenon tube 1, of the Fresnel lens 3 is a Fresnel surface, and the other surface is a flat surface perpendicular to the optical axis.
The optical axes of the xenon tube 1, the reflector 2, and the Fresnel lens 3 coincide with the optical axis 9 of the illumination device 10. In other words, these optical axes have a coaxial relationship with the optical axis 9.
Of light beams emitted from the xenon tube 1, a light beam propagating in a direction opposite to the object is reflected by the reflector 2 in the direction of the object, and is refracted by the Fresnel lens 3 to illuminate a phototaking range of the phototaking lens 7. On the other hand, of the light beams emitted from the xenon tube 1, a light beam propagating in the direction of the object is directly incident on the Fresnel lens 3, and is refracted by the Fresnel lens 3 to illuminate the phototaking range of the phototaking lens 7.
Although a spherical aberration is compensated by the Fresnel lens 3 shown in FIG. 17, a sine condition cannot be compensated (the Fresnel surface cannot simultaneously compensate the spherical aberration and the sine condition).
For this reason, in order to evenly and satisfactorily illuminate the phototaking range of the phototaking lens 7, as shown in FIG. 16, the optical axis 9 of the illumination device 10 is aligned to be parallel to the optical axis 8 of the phototaking lens 7, and as described above, the optical axes of the xenon lamp 1, the reflector 2, and the Fresnel lens 3 are caused to coincide with the optical axis 9 of the illumination device 10.
As described above, in the conventional illumination device, in order to evenly and satisfactorily illuminate the phototaking range of the phototaking lens, the optical axis of the Fresnel lens must be caused to coincide with the reference optical axis of the illumination device, and the flat surface of the Fresnel lens must be set to be perpendicular to the lens optical axis. For this reason, the design of the camera main body and, especially, the outer shape of the camera front surface (at the side of the phototaking lens), are considerably limited.
In other words, when the optical axis of the Fresnel lens is simply tilted from the reference optical axis of the illumination device or the flat surface of the Fresnel lens is simply tilted (inclined) from the plane perpendicular to the lens optical axis to give priority to design of the camera main body, the projection direction is offset vertically or horizontally. For this reason, the phototaking range of the phototaking lens cannot be evenly and satisfactorily illuminated, and uneven illumination occurs.
In order to eliminate the above-mentioned drawback, it is theoretically possible to design the surface, on the object side, of the Fresnel lens to be a spherical surface so as to compensate a sine condition, or to design the Fresnel lens not to have a rotation-symmetrical shape with respect to its optical axis so as to avoid the projection direction from being offset. However, it is difficult to achieve a process itself required for working the surface, on the object side, of the Fresnel lens to a spherical surface or for working the entire shape not to be a rotation-symmetrical shape, and it is also difficult to assure required working precision. For these reasons, it is impossible to take the above-mentioned countermeasures in practice.